The subject invention relates to a new and improved universal LCC test socket assembly for temporarily connecting the conductive leads of an LCC surface mounted device to an electric testing device during a test and evaluation procedure.
The term LCC is intended to include leaded chip carriers or chip carrier packages that typically consist of one or more circuit chips mounted on a lead frame and encapsulated within an electrically non-conductive housing. In one exemplary type, the encapsulating housing is of a plastic or plastic like material, hence the designation PLCC for plastic leaded chip carrier. In another exemplary type, the encapsulating housing is of a ceramic or ceramic-like material, hence the designation CLCC for ceramic leaded chip carrier.
In the manufacture and use of integrated circuits ("IC") packaged as surface mounted devices, it is important to electrically test such devices accurately, reliably, and quickly. In the LCC device, the IC circuit is contained in a non-conductive housing having a generally square or rectangular, box-like configuration. Generally speaking, LCC packages house memory and microprocessor integrated circuit chips requiring large numbers of conductive leads. LCC's typically include either two rows of conductive leads or terminals along opposed parallel sides of the housing or four rows of conducting leads, one along each side of the housing. The most common configuration of LCC's include four rows of conductive leads contained on either a generally square or rectangular, box-like housing. The conductive leads of a LCC are relatively flexible and extend laterally outwardly from the housing of the semiconductor circuit and are bent downwardly and inwardly, so that the leads curl under the housing of the semiconductor circuit. At such time, the leads are disposed generally in a common plane. A typical LCC may have from 20 to 84 terminals or conductive leads arranged in four equal groups along each side of the housing. For example, a 20-lead LCC has five leads per side. The conductive leads are typically positioned on 0.050 inch centers along each side of the LCC, with each lead having a side portion exposed at the bottom of the housing.
A LCC is designed to be mounted directly on the surface of a circuit board or within a suitable receiving socket of a circuit board, hence the designation surface mounted device. A LCC is typically mounted on the surface of a printed circuit board using a soldering technique to mechanically and electrically attach each conductive lead to a respective solder land on the printed circuit board.
The LCC can be distinguished from dual-in-line packaged (DIP) integrated circuits in that DIP devices are intended for mounting with leads, or more commonly connecting pins, passing through the surface of the circuit board (or within a suitable socket) as opposed to mounting on the surface of the circuit board. Additionally, DIP's typically include only two rows of parallel connecting leads, in contrast to the usual four-rows of conductive leads of the LCC.
Due to the ever increasing use of LCC's, it has become desirable to provide a test socket assembly that may be used to make electrical connections with each of the conductive leads of a LCC surface mounted device for signal testing and/or signal injecting purposes. Because the conductive leads are located along each of the four sides of the LCC, prior art test assemblies for DIP packages generally could not be used effectively even if appropriately sized since they would permit electrical connections with conductive leads at only two opposed sides of the LCC.
Of critical importance, when designing a LCC test socket assembly, the LCC leads tend to be very soft, flexible and hence delicate. For instance, the conductive leads contained within LCC surface-mount devices are frequently provided with solder joints which are sensitive to external pressures and therefore any ensuing contacts with a testing assembly should be carefully conducted so as to avoid fracturing the solder joints. A force component as small as a few grams in a direction parallel to the plane of the LCC could result in fracture of the solder joints of each conductive lead. A single lead of an LCC damaged in testing can render the entire LCC unsuitable for use.
Still another critical design consideration is the alignment system which is utilized in the test socket assembly for aligning the LCC conductive leads with the appropriate contact points of the testing apparatus. Misalignment of the LCC leads from the appropriate contacts on the testing apparatus could render the entire testing procedure useless.
Yet another critical design consideration is the adaptability of the testing apparatus to be capable of testing different configurations of LCC's, i.e., square as well as rectangular configured LCC's.
In summary, there exists a requirement in the electronics industry for a universal test socket assembly for testing LCC packages which have large numbers of fragile conductive leads. The need for such a test socket assembly is especially critical because of the expanding use of LCC surface-mount packages, and the fact that such packages are presently particularly difficult to test. LCC devices are difficult to test because the LCC packages can easily become skewed from a square position relative to the test circuit board, and because of the need to avoid undue pressure contact between the conductive leads of the LCC and the conductive contacts of a test assembly. There is also a need for a universal test assembly that does not cause undue delays during testing and is readily adaptable for testing LCC integrated circuit packages mounted in various patterns on different configured housings.
It is therefore a primary object of the invention to provide a universal test socket assembly for both square and rectangular configured LCC's.
A further object of the subject invention is to provide a universal LCC test socket assembly which does not bend or fracture the delicate LCC leads of a LCC during a test procedure.
Yet another object of the subject invention is to provide a universal LCC test socket assembly which properly positions and holds a LCC while aligning the respective conductive leads with the appropriate electrical contacts on the test socket assembly.
Still another object of the subject invention is to provide a universal LCC test socket assembly which provides an electrical test assembly that can be connected with, and disconnected from, a LCC packaged IC with a relatively small amount of force being applied to the conductive leads of the LCC.
A further object of the subject invention is to provide a universal LCC test socket assembly which readily achieves electrical interconnection between the leads of the LCC and the testing circuit, without subjecting the conductive leads to excessive forces that could result in damage to the leads.
Still a further object of the subject invention is to provide a universal LCC test socket assembly that is inexpensive to manufacture, and can be readily operated by unskilled labor.